The evolution of telecommunication has leaded changes both in the access network and in the core/services network. Long Term Evolution (LTE) and IP Multimedia Subsystem (IMS) are respectively the main examples of this evolution.
LTE is the natural upgrade path for carriers with both GSM/UMTS (Groupe Speciale Mobile/Universal Mobile Telecommunications System) networks and CDMA2000 (Code Division Multiple Access) networks. IMS core network is the evolution of Mobile Softswitch Solution (MSS) core network where the telephony services are provided through AS (Application Server).
IMS network is able to provide telephony services regardless of access technology (e.g. 3G (third generation), LTE, WiFi) although when LTE access technology is used high quality of service can be guaranteed especially for real-time services. VoLTE (Voice over LTE) is the main example of real-time service. A VoLTE call can be seen as an IMS VoIP (Voice over IP) call using the LTE access network.
GSMA (Groupe Speciale Mobile Association) in Permanent Reference Document (PRD) IR.92 [IMS Profile for Voice and SMS Version 8.0, 18 Sep. 2013] defines specific profiles for control and media planes of voice service on LTE.
From a lawful interception point of view a network operator shall provide access to the intercepted Content of Communications (CC) and the Intercept Related Information (IRI) of the mobile target and services related to the target (e.g. Call Forwarding) on behalf of Law Enforcement Agencies. The Law Enforcement Agency (LEA) provides the intercept request (e.g., lawful authorization or warrant) to the CSP. The intercept request identifies, at a minimum, the target, the type of intercept (i.e., IRI-only, or IRI and CC) that is authorized, the authorized period for interception, and the LEA delivery address(es) for the intercepted information.
Telecommunications Service Provider (TSP) must help Law Enforcement Agency (LEA) in conducting lawfully authorized electronic surveillance in Telecommunications Networks. IP Multimedia Subsystem is able to provide multimedia services regardless of access network. In particular access information for VoLTE is provided by the Evolved Packet System, EPS, domain. Service information is provided by IMS. This is due to the different architecture, which is intended to offer more flexible multimedia services in an access independent way. From a lawful interception point of view the access independence of IMS network could lead to a duplication of interception information if both EPS and IMS domains are intercepted.
Indeed even if the same target is used to intercept a user on EPS and IMS domains, the intercepted information are reported with different correlation numbers from involved Network Elements and so the Mediation Function, MF, cannot correlate or filter them out.
The main drawback of this way of working is a useless duplication of intercepted information. Moreover since often a VoLTE call is encrypted into the access network, without a proper correlation the Law Enforcement Agency has no way to recognize it and so filter it out.